fixed error where setNeedsDisplay needs to be on the main queue along wi...

Hi,

Working with your api and found an issue with updating the progressCounter inside another block other than the main queue.  I have provided the fix and a example in your ViewController of the fix.  The issue is if someone is calling the progressCounter in a different thread, drawRect will not get called because it's on the main thread. See http://stackoverflow.com/questions/8313246/setneedsdisplay-not-working-inside-a-block for more details.